This error is commonly referred to as a "single matching error" and occurs when your Product ID (UPC, EAN, JAN, ISBN, etc.) corresponds to the Product ID of an existing ASIN; that is, some of the information you are submitting contradicts the product information (title, brand, colour, size, etc.) that is already present for that particular ASIN.
The provided SKU conflicts with the Amazon catalogue. The standard product ID value(s) provided for this SKU correspond to the ASIN; however, some information is in conflict with the Amazon catalogue. The conflicting attribute values(s) are: Brand (Merchant: [MERCHANT_VALUE]/Amazon: [AMAZON_VALUE]). If your product has this ASIN, modify these attributes to reflect the Amazon catalogue values. If your product has a different ASIN, check if the standard product ID value(s) are correct.
If the information in the Amazon catalogue for this product appears to be incorrect, contact Seller Support.